The objective of this study is to further our understanding of the mechanisms by which cells in the retina make precise synaptic connections with cells in other parts of the visual system, primarily in the optic tectum. Selected populations of ganglion cell axons in the goldfish retina will be filled with the histochemical marker, horseradish peroxidase (HRP), and the individual filled axons will be traced from their retinal origins to their terminal arbors in the tectum. The relative positions of individual axons will be observed at different points along the legnth of the axons and compared with the positions of their terminal arbors in the tectum. These observations will be used to determine the relationship between the path of a ganglion cell's axon to the tectum and the position of its terminal arbor in the tectum. Measurements of the size of the terminal arbors and of the amount of overlap between those from neighboring ganglion cells will also be made and used to determine the area of the tectum receiving information from one region in the visual world and also the accuracy with which axons must be guided to their terminal locations. Similar observations will be made on axons regenerating to the tectum, after damage to the optic nerve, to determine the similarities between normally developing and regenerating axons. This information will be used to evaluate proposals for the mechanisms which guide successful formation of retino-tectal connections.